The present invention relates to a dispenser for dispensing a liquid material. The invention is particularly useful for dispensing medicaments at small, precisely-controlled rates, and is therefore described below with respect to this application.
There are many applications requiring the dispensing or delivering of a liquid at predetermined, precisely-controlled rates. One application requiring particularly precise rates of delivery is a system for administering insulin or other medicaments, and very precise miniature pumps have been devised for this purpose. However, such pumps are expensive to produce and maintain, and/or are inconvenient to refill with the periodic dosage requirements.
It has been previously proposed, particularly in such applications, to use an arrangement for subjecting the liquid to a pressurized gas to force the liquid from the container. Examples of such known systems are illustrated in U.S. Pat. No. 3,640,277 disclosing a gas cartridge for supplying the gas pressure, U.S. Pat. No. 3,468,308 disclosing an inflated bladder for supplying the gas pressure, U.S. Pat. No. 3,871,553 connectible to a compressed air hose for supplying air pressure, and U.S. Pat. No. 2,545,017 disclosing an arrangement for generating the gas by a chemical reaction. Such arrangements, however, generally suffer from the same drawbacks mentioned earlier, namely expensive to produce and maintain, and/or inconvenient to refill. In addition, such known arrangements generally require a valve which must be precisely controlled in order to control the rate of delivery of the liquid to be dispensed; and precise control is extremely difficult when very low rates of delivery are required as in the case of the delivery of insulin or other types of medicaments.